send_file() in lib/filelib.php when using content-ranges attempts to open the file except uses $filename instead of $path

current:
$handle = fopen($filename, 'rb');
byteserving_send_file($handle, $mimetype, $ranges, $filesize);

fix:
$handle = fopen($path, 'rb');
byteserving_send_file($handle, $mimetype, $ranges, $filesize);